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Travel models are built on assumptions about basic travel behavior and patterns of people, groups, and firms. The most basic assumption in trip-based (opens new window), activity-based (opens new window), and freight models (opens new window) is that travel is a derived demand (opens new window), or that it is generated in response to people satisfying personal needs and desires. The activities people might pursue fulfil a variety of needs, which have been commonly represented by Maslow’s  hierarchy of needs (opens new window). When individuals travel to specific locations at certain times, they are engaging in activities like work (satisfying the need for resources), socializing (belonging and esteem), recreation and leisure (self-actualization), etc. Travel behavior is the process people use to organize their time to meet these needs under a variety of constraints (e.g., time, cost, social obligations).
Travel behavior is a broad topic that touches many aspects of travel demand modeling and forecasting. Kostas Goulias has stated that travel behavior modeling:
...refers primarily to the modeling and analysis of travel demand on the basis of theories and analytical methods from a variety of scientific fields. They include, but are not limited to, the use of time and its allocation to travel and activities, the use of time in a variety of time contexts and stages in the life of people, and the organization and use of space at any level of social organization, such as the individual, the household, the community, and other formal or informal groups.
Some basic assumptions are often used when analyzing travel behavior. In some cases, these are generalities built from observed behavior or simplifications of complexities of human behavior. Common assumptions include the following:
- People experience disbenefits (negative utility (opens new window)) for additional time and money spent travelling. Humans have limited time in their days and trade-off travel for participating in other possible daily activities. Travelers will choose shorter travel time paths, all else being equal. Similarly, travelers will chose lower cost ways of travel over higher cost ways.
- Individuals are rational decision makers who seek to optimize benefits to themselves (i.e., maximize their utility (opens new window).
- An individual with a higher income will tend to be less sensitive to travel cost than an individual with lower income.
- Travelers are attracted to locations with a large amount of households and jobs and will tend to travel further distances to these locations than lower density areas.
- Single occupancy vehicle travel is generally preferred over transit, even after accounting for time and cost of travel.
Many travel behaviors change over time and across cultures. For this reason, Travel Survey Data (opens new window) is collected on a periodic basis to understand the local and temporal context of travel behavior. Modelers must be careful not to imbed behavioral assumptions into models that may change over time when forecasting.
To the extent that is possible, travel behaviors should be treated often as sensitivities in the model so that a range of scenarios are predicted, realizing that certain behaviors are not precise mechanical operations, but malleable based on many possibly unknowable factors. One role of the modeler, then, is to identify how travel will be impacted if certain behavioral trends continue or cease.
Activity-Based Models (opens new window) depict the time tradeoffs among activities and travel in the day.
There are several recent papers and reports which present fairly comprehensive overviews of current trends in travel behavior research, including Emerging Issues in Travel Behavior Analysis (opens new window) by Pendyala and Bhat, and Travel Behaviour: A review of recent literature (opens new window) by Curtis and Perkins which are both available online. A more recent review by Buliung and Kanaroglou is also available (opens new window) but requires a subscription to access. These reviews taken together provide a solid foundation to understanding the current state of travel behavior research
# Topics in Travel Behavior
# Representations of Decision Making Behavior in Travel Modeling (opens new window)
Decision-making is a central element of traveler behavior modeling. Many of the behaviors represented in travel demand model are directly related to a decision making process - from choosing travel modes to selecting routes to reach a destination. The way in which these decisions are modeled, however, varies greatly for different decisions and in different model frameworks. The most common form that decision making behavior takes is that of the discrete choice model. However, many other decision making behaviors are utilized in travel models, including heuristic methods, or processes derived from artificial intelligence such as the computational process model.
# Activity-Travel Planning and Decision Making Behaviors (opens new window)
Activity-travel planning behaviors generally refer to the behavioral processes by which individuals plan, schedule and implement their day-to-day activity and travel plans. The topic of activity-travel planning encompasses many different traveler behaviors, from activity conception/generation, to the decision-making processes by which the activity plan is carried out. These behaviors are represented in various conceptional models of activity planning behavior, and are implemented in many activity-based models.
# Joint Travel Behavior (opens new window)
Joint Travel Behavior refers to how people choose to travel when considering the travel of other household members or persons in their social networks. For instance, children under driving age need to be driven to activities by parents, which requires coordination of household schedules. Household members often need to decide how to share vehicles to conduct daily activities. Some activities are more likely to be conducted with other people, like eating a meal or socializing, whereas other activities may often be conducted alone, such as commuting to work.
# Other Resources
TRB supports a committee on travel behavior and values (opens new window). The committee is concerned with promoting research and disseminating research results on traveler values, attitudes, and behavior. Traveler values and attitudes refer to motivational, cognitive, situation and disposition factors determining human behavior. Traveler behavior refers primarily to the modeling and analysis of travel demand, based on theories from a variety of scientific fields. These include but are not limited to time use and activity-based approaches, longitudinal methods, and spatial behavior. The committee serves as a forum for the development, testing, and dissemination of new interdisciplinary methods of inquiry. If you are interested, please visit the TRB Traveler Behavior and Values committee website (opens new window)
Another significant resource in the field is the International Association of Travel Behavior Research (opens new window). This group consists of the leading researchers in the field of traveler behavior. It hosts triennial conferences where the latest research in field is presented and publishes selected works from each conference in a conference book. More information on IATBR can be found at www.iatbr.org (opens new window).
Other pages on this website include:
- Travel Behavior of Diverse Populations
- Using policy to affect travel behavior
- Long Distance Travel Behavior (opens new window)
- Travel Behavior Resources (opens new window)
Maslow, A (1954). Motivation and personality. New York, NY: Harper. p. 236. ISBN 0-06-041987-3. ↩︎
Goulias, Kostas http://onlinepubs.trb.org/onlinepubs/millennium/00136.pdf (opens new window) ↩︎